Mixer for mixing potentially explosive materials



July 25, 1966 R. J. BALAzER 3,262,680

MIXER FOR MIXING POTENTIALLY EXPLosIvE MATERIALS Filed Sept. 24, 1963 5Sheets-Sheet 1 INVENTOR. RlcHARD J. BALAZER di M ATTORNEYS BY ww/W July26, 1966 R. J, BALAZER 3,262,680

MIXER FOR MIXING POTENTIALLY EXPLOSIVE MATERIALS Filed Sept. 24, 1963 :5Sheets-Sheet 2 ln In INVENTOR RICHARD J. BALAZER ATTOBNEYS' July 26,1966 R. J. BALAzER MIXER FOR MIXING POTENTIALLY EXPLOSIVE MATERIALSFiled Sept. 24, 1963 5 Sheets-Sheet 3 RAISE C |07 LOWER LSl gl Uff@ [O8JJ IF INVENTOR. RICHARD J. BALAZER ATTORNEYS United States Patent O3,262,680 MIXER FOR MIXING PGTENTIALLY EXPLGSIVE MATERIALS Richard J.Balazer, Saginaw, Mich., assignor to Baker Perkins Inc., Saginaw, Mich.,a corporation of New York Filed Sept. 24, 1963, Ser. No. 311,193 13Ciaims. (Cl. 259-104) This invention relates to mixer construct-ions andmore particularly to mixers having bowls which are raised to immersemixers extending from a mixer housing inthe contents of the bowl. Such amixer is shown and described -in United States Patent No, 3,075,746,granted January 29, 1963, to Leon Yablonski and James W. Strouse, and isparticularly useful for mixing highly reactive and potentially explosivematerials such as high energy fuels. Since such fuels normally containtheir own oxygen supply, they are ignited very easily and burn veryrapidly. When mixing fuels of this type, safety requirements dictatethat the bowls seal tightly to the mixer housing and that the mixingoperation be performed at subatmospheric pressure in the absence of air.If the howl can lbe quickly removed from the mixer housing, should thecontents commence to bum, so that the pressure condition b-uilt upquickly by the burning fuel is relieved, an explosion which wouldotherwise damage the mixer, and the bowl lifting elements particularly,can usually be avoided.

One of the prime objects of the present invention is to provide sensingmeans for determining that a dangerous explosive condition exists duringa mixing operation of the character described and for immediatelydisabling the mechanism holding the bowl to relieve the press-urecondition which occurs and to provide access to the f-uel.

A further object of the invention is to provide mechanism of thecharacter described which is operable to decelerate and cushion thesharp downward movement of the bowl, once it has been moved from theimmediate vicinity of the mixer housing.

A further object of the invention is to provide mechanism of thecharacter described which may be incorporated in a mixer having levelingmeans for insuring that the bowl is moved upwardly to the mixer housingin a level condition.

Briey, the invention is concerned with a mixer having a bowl which israised to enclose the mixer members and sensing means which isresponsive to a potentially explosive condition -in the mixer to disablethe means supporting the bowl in operative position so that the heavybowl can quickly drop. The invention is also concerned with the mannerin which the speed of descent of the bowl is decelerated after it hasdropped a predetermined distance and the manner in which the bowlleveling means is incorporated so that it does not interfere with therapid drop of the bowl, when a rapid drop becomes necessary.

A further object of the invention is to provide mechanism of thecharacter described which is highly reliable and edicient in operationand relatively compact and simple in nature.

Still a further object of the invention is to dcne mechanism of thecharacter described which can be easily and economically manufacturedand applied to existing mixer installations, as well as to newinstallations.

Other objects yand advantages of the invention will he lCe pointed outspecifically or will become apparent from the following description whenit is considered in conjunction with the appended claims and theaccompanying drawings', in which:

FIGURE 1 is a front elevational view of the mixing machine, with thediagrammatic lines indicating a lowered position of the bowl raising andlower-ing cylinders and bowl;

FIGURE 2 is a partly sectional, schematic, side elevational viewillustrating the hydraulic system for operating 'the bowl raising andlowering mechanism; and

FIGURE 3 shows a typical electrical circuit for controlling thehydraulic system operating the bowl raising and lowering elements.

Referring now more particularly `to the accompanying drawings, a mixingmachine is depicted which, as in the aforementioned patent, has a base10 supporting upright side wall casings 11, a rear wall casing 12, and atop wall casing 13. Provided on the top wall casing 13 on a platform 14is a motor 15 having an armature shaft 16 mounting a drive pulley 17, asshown. The pulley 17 is connected to a p-ulley 18 mounted fast on theinput shaft 19 of a speed reducer 20 through a belt 21, and the outputshaft 22 of the speed reducer 20 is connected to a drive shaft 23 by acoupling 24. The drive shaft 23 may be connected with intermeshing mixerblade members M-1 and M-Z mounted on shafts S-1 and S-2 driven by thedrive shaft 23 in exactly the manner shown in the aforementioned UnitedStates Patent No. 3,075,746.

A dependent tubular housing H is secured to the top casing 13 as withbolts 25 and comprises an upper shell 26 and a lower shell 27 which arebolted together as at 28. As in the aforementioned patent, the housing His provided with a lower flange 29 having side ears 30 which mountdepending loca-tor pins 31. The front side of the mixer machine is opento permit a bowl B to be moved into position under the housing H andgenerally such a bowl B will be mounted on wheels and tracks will Ibeprovided leading in under the housing H. These elements form no part ofthe present invention and are not shown in FIGURE l. A flange 32 is alsoprovided on the upper end `of the bowl B and is provided with ears 33having openings 34 for receiving the locator pins 31 when the Ibowl B israised upwardly to sealed engagement with the housing H in a mannerwhich will be described. It is Ito be understood that the constructionof the anges 29 and 33 may be identical with the construction of theflanges of the mixer disclosed in the aforementioned patent, and that aseal is provided so that the 'bowl B seals to the lower end of them-ixer housing H when it is brought up into engagement with it. Thehousing H is similarly a sealed housing, and is in sealed engagementwith the top casing 13 in the manner illustrated in 'the patent to whichI have referred.

Provided on the bowl B are brackets 35 having openings 36 to receive thelocator pins 37 on lift arms 38. Each of the lift arms 38 is secured toa gusseted bracket 39 which is bolted as at 40 to the upper end of apis-ton 41. It will be noted that a double acting hydraulic cylinder 42is provided on one side of Ithe mixer and -a like double actinghydraulic cylinder 43 is provided on the other side of the mixer, andeach receives a piston rod 41 mounting a piston 44 on the lower endthereof. The line 45 for supplying oil under pressure to the cylinder 42for forcing its piston 44 @ber 55 formed therein as shown.

downwardly is shown at 45, and the line 46 for supplyingy oil to thecylinder 43 lto force its piston 44 downwardly is similarly provided atthe upper end of cylinder 43. The cylinders 42 and 43 may beconventional, double acting hydraulic cyl-inders of the typemanufactured by Vickers Incorporated of Detroit, Michigan, U.S.A., ModelNo. FL-24-PS-20.

At their lower ends each of the cylinders 42 and 43 connects with avertical cylinder member generally designated 47 which is closed at itsupper end. In FIGURE 1 a fitting 48 is illustrated which may be providedat the lower end of each cylindrical member 47 and, as shownschematically in FIGURE y2, housed within the fitting 48 is a tubulardifferential area, piston member 49 having a tapered nose portion 49awhich in one position of piston member 49 seals the fitting as shown, areturn spring 50 extending into each tubular piston 49 and bearingagainst the rear wall of the fitting 48 as shown. Intermediate its ends,each cylinder 47 is provided with a valve seat 51 for a ball checkmember 52 as shown, there being an opening 53 permitting the entry offluid from the lower chamber 54 formed in each cylinder 47 to the uppercham- Normally each chamber 54, the lower portion of each chamber `55,and each fitting 48 is lled with oil O. The springs 50 have littlestrength and the dilerential area between the front and rear surfaces ofeach piston 49 assures that each piston 49 is normally in the closedposition in which it is shown in FIGURE 2, whether oil is being fed tothe upper ends of the cylinders 42 and 43 through lines 45 and 46,respectively, or to the lower ends thereof through lines 56 and 57,respectively.

As will be presently explained, it is when the oil pressure behindpistons 49 is relieved and piston rods 41 are moved downwardly under thefull weight of the bowl B that the pistons 49 are displaced and the oilin chambers 54 is forced upwardly to displace and compress the nitrogengas G which is provided in the upper ends of cylinders 55 under apressure of about 50 p.s.i. Valves 55a are provided in the upper ends ofcylinders 47 to permit the nitrogen gas to be charged to cylinders 47 inthe rst place.

To maintain the bowl B level as it is being raised and lowered, a leveladjustment system is provided which includes an elongate tape 58 (seeFIGURES tl and 2) trained around a pulley 59 supported by the piston rodof cylinder 42 and a pulley 60 `supported by the piston rod of cylinder43. The pulleys 59 and 60 may be supported by arms l61 which projectinwardly from the brackets 38. At one side of the frame of the machine,mounted on a side casing 11, is a level adjusting valve box 62 in whichis housed a lever 63 (see FIGURE 2) which is pivotally mounted withinthe Ibox at 64. The lower end of tape 58 is secured to the lever 63 :andit will -be seen that the lever is connected `to a coil spring 65secured within the box 62 as at 66. A length adjusting member 64 isprovided in the tape 58 so that adjustments in tape length are possible.

It will be seen that lever 63 includes 'a pair of arms 63a and l63bwhich operate normally open hydraulic valves 67 and 68, respectively.These valves may =be the Model TT-24160-O cam operated two way valvesmanufactured by Double A Products Co. of Manchester, Michigan, U.S.A. Atits opposite end the tape 58 is coupled, as at 69, to the piston rod 70of yan air cylinder 71 which is at all times supplied with iluid under apredesignated pressure, such as 100 p.s.i., through a line 72. Thesignificance of connecting the end of the tape 58 to the piston 70 willlater be explained.

Normal raising and lowering of the pistons 41 to raise vand lower thebowl B is accomplished through a normally neutral four way, doublesolenoid hydraulic valve 73 which may be a Model XDG4S4-0l2C-4l valvemanufactured by Vickers Incorporated. Lines 74 and 75 normally connectthe valve 73 with a pump P and a reservoir 76, respectively. The pump Pis one having a pressure control 77 and may be the variable volume pumpwhich is included in the Vickers hydraulic power package ModelTZO-BIOC-Gel() manufactured by Vickers Incorporated which includes anelectric motor 78. From the Valve 73 a line 79 leads to the lines 45 and46, and a line 80 leads to a manifold line 81 to which lines 82-85connect. 'It will be seen that each of the lines 82 and -84 connect withthe line 56, and each of the lines 83 and S5 connect with the line 57.In addition, a line 86 leading to the valve 67 connects with the line84, and a line 87 leading from the valve 67 connects with the line 85.Also, a line 88 leading to the valve 68 connects with the line 83, and aline 89 leading from the valve 68 connects with the line 82. It will beseen that pairs of ball check valves are provided in the lines 82-85(the arrows pointing in the direction in which tiow is permitted) whichinsure that all iluid proceeding to the lower ends of cylinders 42 and43 proceeds rst of all to the valves 67 and 68.

Mounted on the one side casing 11, as shown in FIG- URE l, is a normallyclosed electro-pneumatic pressure responsive switch 90, which may be .aModel DIX*IIl8-SS manufactured by Barksdale Valves, of Los Angeles,California, U.S.A. The switch 90, which maybe setto open under apressure of l p.s.i. above atmospheric pressure, communicates with theinterior of housing H through a line 91, and when the pressure build-upin housing H indicates that the fuel being mixed is burning, thenormally energized solenoid 92 of a hydraulic valve 93, which may be theModel XDG4S4-0l2A-4l valve manufactured by Vickers Incorporated isdeenergized and the hydraulic system permits the bowl B to drop sharplyaway from the housing H in a lmanner which Will be shortly described indetail. A line 94 connects with the valve 93 to divert oil thereto fromthe line 74 communicating with pump P, and a line 95 leads from valve 93to the reservoir 76. 'Leading .from the valve 93 is a pipe `96connecting with a line 97 communicating with the `fitting 48 adjacent tocylinder 42, and a line 9S leading to the tting 48 adjacent to cylinder43. The line 96 is connected to a standpipe `96a by a safety valve whichopens only when normal operating pressure is exceeded in the lines 97and 98 and it will be seen that line 95 connects with the standpipe 96a.Also communicating with the pipe 96a is a line 99 which leads to theupper end of the cylinder 47 connected with hydraulic cylinder 42 and aline 100 which leads from the standpipe 96a to communicate with thechamber 55 of the cylinder 47 connecting with cylinder 43. Sight gauges101 may be provided in each of the lines 99 `and 10G, and branch lines102 connect each of the lines 99 and 10d with the chambers 54 of thecylinders 47.

In FIGURE 3 I have shown a wiring diagram which comprises line wires L-1and L-2 connected wit-h a suitable source of current. A limited switchLS-1 is provided in a cir-cuit line a and a circuit line a' includes theraise solenoid 103 of the normally neutral valve 73. A normally closedlimit switch LS2 is provided in a circuit line b spanning lthe linewires L-l and L-2 which also includes the lowering solenoid 104 of valve713. As shown in FIGURE 1, normally open limit switch LaS-'1 is closed'when the bowl B is placed in position under the mixer, and normallycl-osed limit switch LS2, which is held open by the one slide 39 whenthe slide is in down position, closes when the slides or brackets 39 areraised enough to release it. This occurs at the time the locatung pins37 are received in lthe locator openings 36. A third normally open limitswitch LS-3 is provided in a line c which may bridge lines c and a. Inaddition, a push button 105 which normally connects the circuit a with aline d, as shown in FIGURE 3, is provided, and a push button 106 whichnormally bridges the circuit line c 1s also provided. The button 105 maybe actuated to connect the circuit lines c and a', and the button 106may be` actuated to connect the circuit lines d and b. A circuit line ebridges the lines a Iand b. In addition,

-pulleys 59 and 60 the relay R-l which is connected in the circuit linef has normally closed contacts 106a in the line b, and normally opencontacts 107 and 108 in the lines c and f. The normally closed pressuresw'tch 90 is connected in the circuit line f with the normally opencontacts 108 of relay -R-1. A reset button r is provided, as shown, inthe line g which also includes the solenoid 92 of valve 73, and a line gconnects the lines g -and f. Limit switch closes just before the bowl Breaches its upper mixlng position to -keep the raise solenoid 103energized during the mixing operation.

The operation In operation, when a bowl B containing contents to bemixed is transported to the position indicated in diagrammatic lines inFIGURE l under the housing H, the normally open limit switch LS-l isclosed. At this time, limit switch LS-2 is held open by the one slide 39which is in down position. Also, the coil of relay R-l holds thecontacts 107 and 108 closed and the cont-acts 106 open. lf the operatorthen depresses the raise button S to bridge the circuit lines c and a',the raising solenoid 103 is energized through lines a, e, c, and a' andvalve 713 is actuated to provide dow from the line 74 to the line 80 andthrough the 4valves 68 and 67 lto the lines 56 and 57, respectively,which supply the lower ends of cylinders '42 and 43, so that the pistonrods 41 are raised. At this time the lines l45 and 46 leading from theupper ends of cylinders 42 and 43 are connected with the line 75 leadingto the reservoir 76 through the valve 73 in line 79.

When the left (in FIGURE l) slide or bracket 39 is raised suiciently, itmoves beyond the normally closed limit switch LS-Z which closes andfunctions to supply current to the solenoid 103 through circuit lines b,c, and the Ibutton 105 which is held in depressed position. Limit switchLS-2 is so positioned that this occurs at the time the pins 37 arereceived Iby the openings 36. Thus the limit switch LS-2 takes over thefunction of the limit switch LS-l which opens when the bowl B passesbeyond it. Normally open limit switch LS-3 is closed by the left slideor bracket 39 in FIGURE 1 just before the bowl reaches the mixingposition in which -it is shown in solid lines in FIGURE 'l and functionsto keep the raise solenoid 103 energized during the mixing operationthrough lines b, c, and a', even though the button 105 is released.During the mixing operation the pump P with its pressure control 77maintains a constant pressure under the pistons 44 adequate to supportthe weight of thev bowl and its contents. 'For example, the pump mayhave to maintain 750 Ip.s.i. to accomplish this purpose.

During the time that the bowl B is being raised, the are being movedupwardly by the slides or brackets 39, and if -the bowl B should tilt,the leveling adjustment system 62 will be actuated to compensate for thelead or lag of one of the cylinders 42 and 43. If, for instance,cylinder 43 is leading, the lever 63 will be pivoted clockwisely by thetape 58 to actuate valve 67 to partially close oi the ow from line 86through the valve 67 to the line 87 and thereby restrict the llow toline 57. Similarly, if the cylinder 42 should lead the cylinder 43, thelever 63 -is pivoted counterclockwisely and the valve 68 is partlyclosed t-o restrict the flow of uid from line 88 through the valve 68 tothe line 89 and thereby restrict the flow to line 56.

The interior of the housing H is preferably ev-acuated through a lineconnection such as at 109 to a suitable vacuu-m pump. If the mixing ofthe contents of bowl B proceeds normally, the vacuum condition inhousing H is maintianed and the pressure switch 90 remains closed. Thevalve 93 which is actuated by the normally energized solenoid 92normally connects the line 94 'with the lines 97 and 98 and normallymaintains the valve pistons 49 in the closed positions in which they areshown in FIGURE 2. To lower the bowl B after a normal mixing operation,the button .106 is depressed to connect circuit lines d and b andenergize lowering solenoid 104. Depressing the button 106 energizessolenoid 104 through lines b, e, a, d, and the button |106. The bowl Bdescends evenly since the level adjustment system 62, in the same manneras previously, takes care of the lead or lag of one of the cylinders 42and 43.

If the contents of the bowl B should commence to burn during the mixingoperation, pressure will build up in the housing H and the pressureswitch is opened. Solenoid 92 and relay R-1 are deenergized and valve 93is spring returned to deactivated position. This has the effect ofcommunicating the lines 97 and 98 with the line leading to the reservoir76 and relieving the pressure behind valve pistons 49. During the mixingoperation the solenoid 103 remains energized, as noted, with a circuitbeing made through lines b, c and LS-3. Deenergization of the relay R41permits contacts 107 to open and contacts 106e to close to deenergizethis circuit and energizes a circuit to solenoid 104 through line b. Thebowl B Will drop sharply because, with the pressure relieved behindvalve piston 49, oil will be forced past the piston 49 to the chambers54 as well las into lines 56 and 57. While the bowl B first free fallsrap' idly as the oil is displaced into chambers 54, which are enlargedby the retreat of Valve pistons 49, the nitrogen gas in chambers 55 is,after an interval, compressed by the oil and the fall of the -bowl isthen cushioned to its normal lowering speed. The switch 90 then bothreverses the valve 73 to its lowering position and operates valve 93 torelieve the pressure behind valve pistons 49. In this way an explosionis avoided which would otherwise damage at least the cylinders 42 and43.

As noted, a pressure of about p.s.i. is maintained in the cylinder 71and the piston 70 gives as soon as the tape 58 is pulled more than isrequired to completely depress the leveling valve 67. No attempt is madeto control the level of the rapidly dropping bowl and it is necessary toconnect the tape in this manner to prevent damage to the level adjustingsystem. When it is desired to operate the mixer again, manually actuateddraining valves 110 are operated to return the displaced oil to thesystem and the reset button r can be depressed to again energizesolenoid 92 and restore the valve 93 to its actuated position. Relay R-lwill 4also be energized, of course, to close contacts 107 and 108 andopen contacts 106e. Returning of the valve 93 to operating position hasthe effect of opening the tlow of oil through the line 94 to the lines97 and 98 to restore the oil pressure behind valve pistons 49 and permitnormal operation of the mixing machine once again.

Various other conventional valves are provided in the system as shown.For instance, the valves 111 are leakage drain valves which are barelycracked open. The valve 112 is a safety relief valve which may be set toopen at 850 p.s.i. when normal line pressure is 750 p.s.i. and thus haveno effect on normal machine operation. However, if pressure switch 90 orvalve 93 should fail or delay in operating during an explosion, valve112 allows pistons 49 to rapidly pass oil to chambers 54 at pressureswell within the strength of the machine. Also, it will be noted that thesystem is fail safe in the sense that the control circuit is broken whenthe pressure switch 90 is actuated. Deenergization of the controlcircuit, as when a power failure occurs, will itself cause safetydropping of the bowl B. With the system described, provision is made foreiiiciently and reliability taking care of emergency situations Withoutrendering the system inoperative.

While I have shown a pressure responsive switch 90 for triggering therelease of the bowl B, I contemplate that other devices may be used. Forinstance, va flame detection device responsive to an orange color or aheat detection device in the form of a dissimilar metal thermostat or aBourdon tube could be employed within the housing H to actuate a switch.The pressure switch shown is preferred because of its low cost and thefact thatV it will detect burning at the bottom of the bowl very rapidlybefore, for instance, the llame is visible to a lame detecting device.

It is to be understood that the drawings and descriptive matter are inall cases to be interpreted as merely illustrative of the principles ofthe invention, rather than as limiting the same in any way, since it iscontemplated that various changes may be made in the various elements toachieve like results without departing from the spirit of the inventionor the scope of the appended claims.

I claim:

1. In a mixer; axially disposed mixer means including mixer elementmeans and bowl means movable relatively axially from a remote positionto an operative position in which said bowl means encloses said mixerelement means; a motor elfecting said axial movement and also exertingan axial force holding said bowl means and mixer means in operativeposition; and means responsive to an abnormal condition in said bowlmeans for disabling said motor to permit rapid return to the remoteposition.

2. In a mixer; an axially disposed mixer housing mounting mixer means;bowl means movable axially from a remote position to an operativeposition surrounding said mixer means; fluid pressure supplied means ateach side of said bowl means for moving said bowl means to operatingposition; means for supplying fluid under pressure thereto; means forrelatively moving said mixer means and bowl means to mix the contents ofsaid bowl means; means permitting said bowl means to move at a -highrate of speed away from said housing in the event of an abnormal mixingcondition; leveling adjustment means including a control member movablewhen one of said fluid pressure supplied means leads or lags the otherfluid pressure supplied means; iluid pressure flow control meansinterposed between said means for supplying fluid under pressure andsaid fluid pressure supplied means and connected to said control memberto be actuated thereby; and means supporting said control memberyieldable when said bowl means moves at a high rate of speed to preventdamage to said leveling adjustment means.

3. The combination dened in claim 2 in which said iluid pressuresupplied means at each side of said bowl means comprises fluid pressureactuated `cylinders having piston rods mounting bowl raising slides;said convtrol member comprises an elongate exible strip connected at oneend to said flow control means and at the other to said means yieldablysupporting said strip; and guides mounted on said slides around whichsaid strip is trained to respond to relative lead or lag of said slides.

4. The combination dened in claim 3 in which said yieldable supportingmeans for said flexible strip comprises an air cylinder having a pistonrod to which said strip is connected.

5. In a mixer; a mixer housing having vertically ex` tending mixermeans; bowl means for sealing to said mixer means movable verticallyfrom a position remote from said mixer housing up into engagement withsaid mixer housing; means for relatively moving said mixer means andbowl means to mix the contents of the bowl means; uid pressure means formoving said bowl means upwardly into engagement with said housing means;means responsive to an increased pressure in said mixer housingdisabling said Huid pressure means and permitting said bowl means todrop under the inuen of gravity; and means incorporated with said iluidpressure means for cushioning the fall of said bowl means after apredetermined interval of drop.

I6. In a mixer for combustible materials; axially disposed mixer housingmeans including mixer means and 'bowl means movable relatively axiallyfrom a remote position to an operative position in which said mixer o omeans is enclosed by said bowl means; means holding said bowl means inoperative position; and means, sensing that the contents of the bowlmeans are burning, reactive to disable said holding means to permitreturn to said remote position.

7. In a mixer for combustible materials; an axially disposed mixerhousing having vertically extending mixer means; bowl means for sealingto said mixer means movable vertically from a position remote from saidmixer housing into engagement .with said mixer housing; uid pressureoperated cylinder means including piston rod means mounting lift annimeans for raising and lowering said bowl means; a source of fluid underpressure and fluid circuit means connecting said source with thecylinder mea-ns; electrical circuitry connectable to a source of powerand fluid circuit elements actuated thereby to move fluid .from saidsource, under pressure, to the lower and upper end of said cylindermeans for raising and lowering said lift arm means and bowl means;auxiliary cylinder means connected with the lower end of sai-d cylindermeans; valve means in said auxiliary cylinder means for discommunicatingsaid cylinder means from the auxiliary cylinder means; line meansconnected with the source of `iluid under pressure communicating withsaid valve means and imposing a fluid pressure on said valve meansurging it to a position normally preventing communication of saidauxiliary cylinder means with said cylinder means during' raising andlowering of said bowl means; means for revolving said mixer means to mixthe contents of the -bowl means; means for maintaining fluid underpressure in the cylinder means to hold said bowl means in raisedposition -in engagement with said housing means during the mixingoperation, and means connected in said circuitry responding to a burningcondition in said mixer housing to relieve the lluid pressure on saidvalve means and permit its displacement to allow fluid from the cylindermeans to enter the auxiliary cylinder means and permit said bowl meansto drop sharply under the inuence of gravity.

8. The combination defined in claim 7 in which said cylinder meanscomprises a pair of hydraulic cylinders.

9. The combination defined in claim 7 i-n which sa-id auxiliary cylindermeans includes gas lled chamber means closed by check valve means.

10. The combination defined in claim 7 in which said means responsive toa burning condition comprises a pressure switch and means is providedfor moving fluid under pressure to the upper end of said cylinder meanswhen said pressure switch is actuated.

11. The combination defined in claim 10 in which said pressure switchhas normally closed contacts connected in said electrical circuitry.

12. In a mixer; an axially disposed mixer housing having verticallyextending mixer means; :bowl means for sealing to said mixer meansmovable vertically from a position remote from said mixer housing intoengagement with said mixer housing; a pair of hydraulic cylinder meansprovided with lift arms for raising and lowering said bowl means; asource of Huid under pressure and means connecting said source with thecylinder means; electrical circuitry connectable to la source of powerincluding elements actuatable to initiate said raising and loweringoperations; pulleys on said lift arms; a tape trained around saidpulleys; iiow restricting valve means connected -to one end of said tapeand interposed between said source and cylinder means to Vary the flowto said cylinder means in accordance with the relative lag or leadthereof as indicated by said tape; a ixed air cylinder having a pistonrod to which the other end of said tape is connected; means forrevolving said mixer means to mix the contents of the bowl means; meansincorporated with said means connecting said source and cylinder meansoperating said cylinder means to hold said bowl means in engagement4with said housing means during the mixing operation; and meansresponsive to an increased pressure in said mixer housing disabling saidReferences Cited by the Examiner cylinder means to permit said bowlmeans to drop sharply under the influence of gravity. UNITED STATESPATENTS 13. In a mixer for combustible materials; mixer hous- 2,036,2657 /1937 Heue et al. 99 238 ing means includinfy mixer element means anda closure 5 for said housing mans movable from a remote position 30757461/1963 Yablonskl et al 259-102 to a closed posit-ion; means holding saidclosure in closed WILLIAM .L PRICE Primary Examiner.

position; and means, sensing lthat the material being mixed is burning.reactive to disable said holding means WALTER A- SCHEEL: Examllwandpermit said closure to return to remote position. l0 ROBERT W JENKINSAssistant Examie,

13. IN A MIXER FOR COMBUSTIBLE MATERIALS; MIXER HOUSING MEANS INCLUDINGMIXER ELEMENT MEANS AND A CLOSURE FOR SAID HOUSING MEANS MOVABLE FROM AREMOTE POSITION TO A CLOSED POSITION; MEANS HOLDING SAID CLOSURE INCLOSED POSITION; AND MEANS, SENSING THAT THE MATERIAL BEING MIXED ISBURNING, REACTIVE TO DISABLE SAID HOLDING MEANS AND PERMIT SAID CLOSURETO RETURN TO REMOTE POSITION.